Create a (json) schema for the VS Code Debug Protocol

[weinand]

Instead of keeping the specification of the VS Code Debug Protocol as a TypeScript d.ts file we should introduce a language neutral json schema for it.

An example for this is the Chrome Debugger Protocol schema:
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/v8_inspector/js_protocol.json
(they are not using a json schema but their own invention).

Ideally we could generate client and server libraries for different implementation languages for this.
So the https://github.com/Microsoft/vscode-debugadapter-node/blob/master/protocol/src/debugProtocol.ts could be a result of this.

For a similar discussion about the Language Protocol see: microsoft/language-server-protocol#25